           result
           (if head-pre-checks
             (do
-              (log/debug (str "head failed prechecks."))
+              (log/debug (str "moreover-head: head failed prechecks for parent: " (get-in parent [:rule])))
               :fail)
             (unify
              (copy parent)

        result
        (if pre-check
          (do
            (log/debug (str "child failed pre-check."))
            :fail)
          (unifyc parent
                  {:comp child}

(defn overc [parent comp]
  "add given child as the comp child of the phrase: parent."

  (log/trace (str "set? parent:" (set? parent)))
  (log/trace (str "seq? parent:" (seq? parent)))
  (log/trace (str "seq? comp:" (seq? comp)))

  (log/trace (str "type of parent: " (type parent)))
  (log/trace (str "type of comp  : " (type comp)))
  (log/trace (str "nil? comp  : " (nil? comp)))

  (cond
   (nil? comp) nil
